Encapsulated barrier for flexible films and a method of making the same

ABSTRACT

The present invention relates to a film structure and a method of manufacturing the same. More specifically, the film structure may include a barrier material made from EVOH, nylon or other thermally sensitive barrier material encapsulated by a first adhesive material. The barrier material and the first adhesive material form a barrier layer and a first set of adhesive layers when coextruded. The barrier layer and the first set of adhesive layers may be coextruded at the same or a similar temperature to form a first extrudate. The extrudate may be encapsulated by or otherwise coextruded with a second adhesive material to form a second extrudate at a higher temperature than the first extrudate that then may be formed into a flat sheet via a die. The first set of adhesive layers protects the barrier layer from high temperatures and long residence times related to the coextrusion/lamination process that may degrade the barrier layer. In addition, acid terpolymer consisting of ethylene/methyl acrylate/acrylic acid adheres a barrier material of EVOH to outer layers of the film structure.

FIELD OF THE INVENTION

The present invention relates to an encapsulated barrier film structureand a method of making the same. More specifically, the presentinvention relates to a thermoplastic, multilayer packaging film having abarrier layer consisting of a thermally sensitive polymer material,preferably ethylene vinyl alcohol. The material acts to prevent thepassage of gases such as, for example, oxygen and/or water vapor, fromone side of the film to the other. The barrier material is encapsulatedby one or more layers of a relatively thermally stable material thatacts to protect the barrier material from high temperatures and/or longresidence times present during coextrusion, lamination or coating thatmay destroy or otherwise degrade the barrier material. The one or morethermally stable encapsulating layers aid in binding the thermallysensitive barrier layer to outer layers having relatively higher meltand/or extrusion temperatures thereby maintaining optical clarity of thefilm produced therefrom. In addition, the present invention relates tousing an acid terpolymer as an adhesive to bind the thermally sensitivebarrier core material to high temperature outer layers while eliminatingclarity problems associated with using other adhesives.

BACKGROUND OF THE INVENTION

It is, of course, generally known to utilize a polymeric material as abarrier material in films to prevent the passage of molecules such as,for example, gases and water vapor. Films may have these barrierproperties to protect foods or other gas-sensitive materials that may becontained within bags or other containers made from the films. Inparticular, food articles are subject to the deleterious effects ofgases and water vapors.

A known film structure that prevents the passage of moleculestherethrough uses polyvinylidene chloride (“PVdC”) or polyvinylidenechloride/methyl acrylate copolymer (“PVdC/MA”), commonly known asMA-Saran and manufactured by Dow Chemical Company. These barriers aregenerally useful in preventing molecules such as oxygen from passingtherethrough but are fairly unstable at the high temperatures needed toproduce many multilayer films from a molten resin. Typically, PVdCdegrades at high temperatures forming polyenes reducing the opticalclarity of films made therefrom. A suitable, albeit more costly,substitute for MA-Saran is ethylene vinyl alcohol copolymer (“EVOH”).

Another film that is commonly used as a barrier layer, especially forfood products such as cheese, is a PVdC coated oriented polypropylene(“OPP”) layer. Structures made using this barrier material have goodbarrier characteristics. Specifically, barrier layers of PVdC coated OPPadequately restrict the movement of oxygen molecules or water vaporthrough packaging made therefrom. However, PVdC coated OPP is costprohibitive.

Generally, EVOH is thermally stable at higher temperatures relative toPVdC or MA-Saran. However, EVOH is still sensitive to high temperatures,particularly when adhered to a layer of polyethylene (“PE”) havingmaleic anhydride functional groups. While EVOH may be extruded at highertemperatures relative to PVdC, the temperature of extrusion may still betoo low for coextrusion with other layers that require very hightemperatures for adequate melting and/or adhesion to lamination orcoating substrates.

Typical methods of coextrusion generally entail feeding the barriermaterial and adhesive resins into a feedblock where they are arrangedinto an “A/B/A” configuration prior to extrusion through a die. Theadhesive layers must be compatible with the barrier layer as well as thesubstrates that are being laminated or coated. Further, the adhesivelayers must be at or greater than 600° F. to adequately adhere to thesubstrates. However, this adhesive layer melt temperature requires thatthe downstream hardware (such as, for example, the feedblock and/or thedie) be at or greater than 600° F. as well. Many barrier materials,including, especially, EVOH, readily degrade when exposed totemperatures greater than about 450° F. for extended periods of time.Due to this degradation, as well as the extensive reaction that mayoccur between the barrier material and the adhesive layer at the layerinterface, the resulting extrudate may have clarity or other problems.For example, EVOH reacts with maleic anhydride, a typical adhesive layerused with EVOH, to produce a “ground glass” appearance when coextrudedat high temperatures for extended periods of time.

A known process of coextruding and laminating heat sensitive materialsis described in U.S. Pat. Nos. 5,106,562, 5,108,844, 5,190,711 and5,236,642, which are hereby incorporated by reference in their entirety.Various methods are disclosed for reducing the impact of highertemperature polymeric meltstream elements on a lower temperaturepolymeric meltstream. The methods may include super-cooling the hottermeltstream element below the melting temperature but above thecrystallization temperature, exposing one or more meltstream elements toan undesirable thermal condition for a limited period of time, and/orusing one or more layers as a heat sink via encapsulation.

Specifically, these patents describe methods of encapsulating one filmlayer by another material. The '562 and '844 patents specifically relateto PVdC or, preferably, PVdC-MA core materials with ethylene vinylacetate copolymer (“EVA”) or ethylene methyl acrylate copolymer (“EMA”)or blend's thereof encapsulating the core material. The encapsulatedPVdC or PVdC-MA is, therefore, protected from the high temperatures ofthe coextrusion process. Generally, the encapsulation method uses anencapsulator having a crosshead mandrel with a central bore to receive afirst meltstream element from an extruder. A second polymeric meltstreamis fed through a sleeve via an inlet passage into the encapsulator. Asthe second meltstream enters the encapsulator, it splits and flowsaround the first meltstream. Consequently, the second meltstreamcompletely surrounds the first meltstream, thereby forming a combinedmeltstream. The second meltstream forms a continuous layer about thecircumference of the first meltstream completely surrounding the firstmeltstream. Thus, the first and second meltstreams maintain theirindividual identities while the first meltstream is completelysurrounded by and encapsulated within the second meltstream. Thecombined meltstream may then be fed through a transport pipe to afeedblock for coextrusion with one or more other layers to produce amultilayer film. However, these patents do not disclose other materialsthat may be utilized as heat sensitive barrier materials besides PVdC orPVdC-MA.

SUMMARY OF THE INVENTION

The present invention relates to encapsulating a barrier material with afirst adhesive layer at the same melt temperature as the barriermaterial. For example, EVOH melts at less than 450° F. and, therefore,is encapsulated by the first adhesive layer at less than 450° F. priorto entering the feedblock. The encapsulating first adhesive layerprotects the barrier material from the hot melt temperatures of a secondadhesive layer, which the first adhesive material encounters within thefeedblock. The first adhesive material insulates the barrier materialfrom the much higher melt temperature of the second adhesive layer.Moreover, the first adhesive material drastically reduces the residencetime of the barrier material within the hardware by keeping it away fromareas of high drag and hangup, such as the internal walls of thehardware. The result is an extrudate with excellent clarity.

It is, therefore, an advantage of the present invention to provide afilm structure and a method of manufacturing the same that use arelatively inexpensive barrier material to prevent the migration ofgases through the film structure such as, for example, oxygen and/orwater vapor, without degrading due to high heat and/or long residencetimes within the film producing equipment. The encapsulated EVOH barrierlayer may be utilized effectively as a replacement to cost-prohibitivebarrier materials such as PVdC coated OPP.

Another advantage of the present invention is to provide a filmstructure and a method of manufacturing the same that allow the use of athermally sensitive barrier material to be utilized within hightemperature coextrusion/lamination processes.

And, an advantage of the present invention is to provide a filmstructure and a method of manufacturing the same that surround thethermally sensitive barrier material with an adhesive in anencapsulating process to protect the barrier material from hightemperatures that may exist in the coextrusion/lamination process.

A still further advantage of the present invention is to provide a filmstructure and a method of manufacturing the same that use an adhesive toencapsulate the barrier material at the melt temperature of the barriermaterial. Further, the adhesive layer may protect the barrier materialfrom layers coextruded therewith or laminated thereto having higher melttemperatures. In addition, the adhesive may protect the barrier materialfrom high temperatures of the hardware and long residence times withinthe hardware.

Moreover, an advantage of the present invention is to provide a filmstructure and a method of manufacturing the same that uses a thermallysensitive material such as EVOH as the barrier layer material to reducecosts of the film structure.

And, another advantage of the present invention is to provide a filmstructure and a method of manufacturing the same that eliminatesinterlayer leakage and deadspots in the barrier layer material flowpatterns.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the detailed description of thepresently preferred embodiments and from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an improved-coextrusion lamination process having aplurality of extruders and encapsulators in an embodiment of the presentinvention.

FIG. 2A shows a film structure having a barrier layer encapsulated byfirst adhesive layers which, in turn, are encapsulated by secondadhesive layers, and then laminated outer substrates in an embodiment ofthe present invention.

FIG. 2B illustrates a film structure having a barrier layer encapsulatedby first adhesive layers and coextruded with second and third adhesivelayers. Further, outer substrate layers are then laminated thereto.

FIG. 2C illustrates an alternate embodiment of the present invention ofa barrier layer encapsulated by first adhesive layers and coextrudedwith a single second adhesive layer on only one side of the barrierlayer/first adhesive layer encapsulation. Further, outer substratelayers are then laminated thereto.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The present invention relates to a film structure and a method ofmanufacturing the film structure. More specifically, the presentinvention relates to a structure having a barrier layer to protectagainst the migration of molecules such as, for example, gases and/orwater vapors. Generally, a first adhesive layer at a relatively low melttemperature encapsulates a thermally sensitive barrier layer. Otheradhesive layers are extruded at high temperatures relative to thebarrier layer and encapsulate or otherwise are coextruded with the firstadhesive layer and the barrier layer. The high temperature of the secondadhesive layers aid in adhering the other adhesive layers to outersubstrate layers. The first adhesive layers may thereby act as both aheat sink to protect the barrier layer from the high temperatures of thecoextrusion/lamination process and a tie layer to aid in bonding thethermally sensitive barrier layer to the outer substrate layers.Moreover, the present invention relates to an improved adhesive layercomprising an acid terpolymer for EVOH that may be used in any hightemperature coextrusion process.

Referring now to the drawings wherein like numerals refer to like parts,FIG. 1 illustrates an encapsulation system 1. The encapsulation system 1may include an extruder 3 that may melt and extrude a barrier material 2into a meltstream 4 using means well known in the art. The barriermaterial 2 may be melted and extruded at a relatively low temperature sothat the barrier material 2 does not degrade within the extruder 3. Anadhesive material 10 may be extruded in a second extruder 9 to form anadhesive meltstream 8. The adhesive material 10 may be melted andextruded at a temperature that is the same or relatively similar to themelt temperature of the barrier material 2. The meltstream 4 may then befed into an encapsulator 6 and encapsulated by the adhesive material 10via methods described in U.S. Pat. Nos. 5,106,562, 5,108,844, 5,190,711and 5,236,642, each of which is incorporated in their entirety byreference. By encapsulating the thermally sensitive barrier material 2(meltstream 4) by the adhesive material (meltstream 8), the barriermaterial 2 may be protected from high temperatures present within thesystem 1. Further, the adhesive material 10 (meltstream 8) may aid inreducing the residence time of the barrier material 2 within thedownstream coextrusion hardware. The residence time is reduced becausethe encapsulating adhesive material 10 increases the laminar flow of thebarrier material 2 through the hardware. In other words, the barriermaterial 2 will not get held up on the surfaces of the downstreamhardware since the barrier material 2 will not contact the surfaces ofthe hardware.

An encapsulated meltstream 12 is thereby produced that may then be fedinto a feedblock 14. The feedblock 14 may be a Cloerene® feedblock, orany other feedblock apparent to those skilled in the art. At this point,a number of different options are available to create a number ofdifferent structures. First, the encapsulated meltstream 12 may beencapsulated by a meltstream 16 from a second adhesive material 18 thatis melted and extruded in a third extruder 15. Partial encapsulation mayoccur if the encapsulating material does not completely surround theencapsulated material. Second, the meltstream 16 and/or a meltstream 17from a third adhesive material 20 that is melted and extruded in afourth extruder 19, may be coextruded with the encapsulated meltstream12 within the feedblock 14. A multilayer-coextruded sheet 22 may beformed after passing the meltstream through a die 21 to thin and spreadthe material into the flat sheet 22. After the sheet 22 is produced, itmay be laminated with outer layers such as various substrates detailedbelow with reference to FIGS. 2A-2C.

FIG. 2A shows an improved structure 100 that may be produced by thesystem described above with reference to FIG. 1. The structure 100 mayinclude a barrier layer 110 that may be completely encapsulated by firstadhesive layers 112. The barrier layer 110 may be composed of anythermoplastic polymeric material that may prevent the migration ofmolecules such as, for example, oxygen and water vapor, therebyprotecting sensitive materials contained within packages made from thestructure 100. For example, the structure 100 may be utilized as a bagthat may be sealed on all sides and may completely surround an articleof food contained therein. The barrier layer 110 may preferably be madefrom a material having superior barrier properties such as, for example,polymers and/or copolymers of EVOH and EVOH blends of nylon orpolyethylene. Moreover, other materials may include polyamide polymers,copolymers and blends thereof; PVdC and PVdC-MA; acrylonitrile polymersand copolymers; and polyethylene copolymers and/or blends.

The barrier layer 110 may be protected by the first adhesive layers 112that may encapsulate the barrier layer 110 via the system described inFIG. 1. The first adhesive layers 112 may be coextruded to encapsulatethe barrier layer 110 to create a first encapsulated extrudate 113composed of a barrier layer 110 completely surrounded by first adhesivelayers 112. The first extrudate 113 may then be coextruded with and/orencapsulated by second adhesive layers 114 at a higher temperature thanthe first encapsulated extrudate 113. The first adhesive layers 112 mayprotect the barrier layer 110 from the high temperatures necessary toadequately melt and extrude the second adhesive layers 114 or any otherlayer coextruded, laminated or otherwise disposed adjacent to the firstadhesive layers 112.

Outer layers 116,118, and/or 120 may be laminated to the first extrudate113 as apparent to those skilled in the art. The outer layers 116,118and/or 120 may include any substrate necessary to add desired propertiesto the structure 100. For example, the outer layer 116 may include anymaterial that may add strength, stiffness, heat resistance, durabilityand/or printability to the structure 100. Further, the layer 116 may actto prevent the migration of certain types of molecules, such as, forexample, moisture, from penetrating into the inner layers of thestructure 100. Further, the layer 116 may add flex crack resistance tothe film structure produced. In addition, the outer layer 120 may becomposed of a material that may act as a sealant when heated. However,it should be noted that the outer layers 116,118 and/or 120 may becomposed of any material apparent to those skilled in the art forproviding desired characteristics to the structure 100.

Alternatively, the first extrudate 113 may be coextruded with one ormore layers as shown with reference to FIGS. 2B and 2C, rather than beencapsulated with the adhesive layers 114. Referring now to FIG. 2B, thefirst extrudate 113 may be coextruded with an adhesive layer 130 on asurface of the first extrudate 113. Another adhesive layer 132 may becoextruded on an opposite surface of the first extrudate 113. Theadhesive layers 130, 132 may be the same material or, alternatively, maybe composed of different materials. The adhesive layers 130, 132 may bedifferent depending on the type of material bonded thereto to form theoutside layers 116, 118 and/or 120. However, any type of layer may belaminated thereon as may be apparent to those skilled in the art.

Further, the first extrudate 113, including the barrier layer 110 andthe first adhesive layers 112, may have an adhesive layer 134 coextrudedon only one surface of the first extrudate 113 as shown in FIG. 2C. Inaddition, there may be no adhesive layer disposed on the oppositesurface of the first extrudate 113. Further, the outer layers 116, 118may be laminated to the adhesive layer 134.

Conventional adhesive layers coextruded, laminated or otherwise disposedadjacent to an EVOH barrier layer typically are composed of a resin ofpolyethylene having maleic anhydride grafted thereon. However, as statedpreviously, maleic anhydride tends to react with the EVOH copolymerchain causing crosslinkages between the maleic anhydride graftedpolyethylene and the EVOH. Many crosslinkages may degrade the quality ofthe barrier layer properties and may further degrade the optical clarityof the film, causing a wavy “ground glass” appearance.

Therefore, other materials may be utilized in the present invention asadhesive layers to encapsulate, coextrude with, laminate to or otherwisebe disposed adjacent to the EVOH barrier material. For example, it hasbeen determined that an acid terpolymer of, preferably, ethylene,acrylic acid and methyl acrylate works well to tie the barrier layer ofEVOH to outer layers of the film structure while protecting the EVOHbarrier layer from high temperatures and long residence times within thecoextrusion hardware. Moreover, acid terpolymer may be used as anadhesive layer for the following barrier layers: EVOH; EVOH/nylonblends; EVOH/polyethylene (“PE”) copolymers; polyamides andacrylonitrile. Although acid terpolymer may not bind well with EVOH,this invention allows the EVOH and acid terpolymer to be subject to longresidence times in order to adequately adhere to each other.

Further, polyamide, otherwise known as nylon, also may adequately bondEVOH to outer substrate layers. Polyamide adhesive layers may adhere tothe following barrier layers at relatively low melt temperatures: EVOH,EVOH/nylon blends, EVOH/PE copolymers and polyamide. Moreover, acidterpolymers and nylon may provide good adhesion to EVOH without causingthe optical clarity problems associated with maleic anhydride.

It should also be noted that while acid terpolymer and nylon may be usedwith encapsulation, as described above, they should not be limited inthat regard. Specifically, acid terpolymer and nylon adhesive layersadhering to EVOH may be used in any film-making process apparent tothose skilled in the art, including coextrusion and laminationprocesses.

Moreover, although maleic anhydride grafted to PE may cause clarityproblems when used as an adhesive with EVOH, maleic anhydride may stillbe used, especially when clarity is not an issue. Polyethylene graftedwith maleic anhydride functional groups may bond to the followingbarrier layers: EVOH, EVOH/nylon blends, EVOH/PE copolymers, polyamidesand PVdC-MA.

Other adhesive layers that may be utilized to bond to the barrier layerand to tie the barrier layers to outer layers may include a polystyreneblock copolymer, preferably for bonding to an acrylonitrile barrierlayer. In addition, ethylene acrylic acid copolymer (“EAA”) may be usedto bond to PVdC-MA or an acrylonitrile barrier layer.

The adhesive layers 114, 130, 132 and/or 134 as shown in FIGS. 2A-2C mayaid in bonding the adhesive layers 112 to substrates that may bedisposed on outside surfaces of the film structure. Generally, theadhesive layers 114, 130, 132 and/or 134 may be melted and/or coextrudedat relatively high temperatures since the adhesive layers 112 protectthe barrier layer 110. The fact that EVOH is protected by the adhesivelayers 112 allows the use of high temperatures to adequately adhere theadhesive layers 114, 130, 132 and/or 134 to the outer substrate layers.

The adhesive layers 114, 130, 132 and/or 134 may comprise any of thefollowing: acid terpolymer; maleic anhydride grafted to polyethylene;EMA; EVA; or polystyrene block copolymer. Further, EMA may be used totie the adhesive layers 112 to the following outer layers: orientedpolyesters; oriented polypropylene; oriented nylon, metal foil; paperand paper board. Further, EVA may be used as the adhesive layers 114,130, 132 and/or 134 to bond the adhesive layers 112 to orientedpolyesters, metal foil, uniaxially oriented polypropylene or highdensity polyethylene (“HDPE”), paper and paper board. Finally,polyethylene such as low density polyethylene (“LDPE”), linear lowdensity polyethylene (“LLDPE”), medium density polyethylene (“MDPE”) andHDPE may be used as the adhesive layers 114, 130, 132 and/or 134 to tiethe adhesive layers 112 to many other types of layers except biaxiallyoriented polypropylene, uniaxially oriented polypropylene or HDPE.

The barrier layer 110, adhesive layers 112, 114, 130, 132 and/or 134 maybe laminated to substrates to form completed film structures. As notedwith reference to FIGS. 2A and 2B, the substrates may include the outerlayers 116, 118 and/or 120. The substrates may be composed of any of thefollowing materials: oriented polyesters and variations thereofincluding metallized polyesters; oriented polypropylene and variationsthereof including metallized PP; biaxially oriented nylon; metal foil;uniaxially oriented PP or HDPE; paper and paper board; non-orientednylon or EVOH/nylon blends, including metallized variations thereof;extrusion coated PET/nylon; single site catalyzed (“SSC”) polyolefinsand ionomers. It should be noted that the list of substrates above isnot exhaustive; any polymeric material may be used as a substrate forany purpose as may be apparent to those skilled in the art. Thefollowing table lists common substrates with materials commonly used asadhesives. Further, the table lists the melt temperatures necessary toadequately adhere the adhesive materials to the substrates:

CONDITIONS FOR ADEQUATE ADHESION TO VARIOUS SUBSTRATES Substrate TypeAdhesive Material (Melt Temperature) PET PE (610° F.), EMA (610° F.)Oriented EMA (550° F.) Polypropylene Foil Acid Copolymer (550° F.),Ionomer (610° F.), PE (610° F.) Paper EVA (550° F.), PE (550° F.),Ionomer (550° F.) Cellophane EVA (550° F.), PE (610° F.) PVDC EVA (550°F.), PB (610° F.) Biaxially Acid Copolymer (550° F.), Ionomer (610° F.),oriented nylon PE (610° F.) Preferred Film Structures STRUCTURE 1 LayerComponents Melt Temperature Outer Layer 118 EVA NA Outer Layer 116oriented polypropylene NA Adhesive 114, 130 EMA, PE or other PE 550-610°F. copolymers Adhesive 112 acid terpolymer or maleic 400-450° F.anhydride grafted to PE Barrier 110 EVOH or EVOH blend 400-450° F.Adhesive 112 acid terpolymer or maleic 400-450° F. anhydride grafted toPE Adhesive 114, 132 EMA, PE or other PE ˜610° F. copolymers Outer Layer120 Polyester NA

As shown in Structure 1 and corresponding to the film structure shown inFIG. 2A or 2B, EVOH or an EVOH blend (>75% EVOH) may be used as thebarrier layer 110 with acid terpolymer or maleic anhydride grafted to PEas the adhesive layers 112 encapsulating the EVOH barrier layer 110. Ina preferred embodiment, the EVOH barrier layer may be encapsulated byacid terpolymer forming the first extrudate 113 at a first temperaturethat is relatively low since both the EVOH and acid terpolymer willextrude within the same temperature range of 400° F. and 450° F.,preferably 410° F. Next, PE copolymers or blends thereof may becoextruded with the first extrudate 113 of EVOH and acid terpolymer ormaleic anhydride to make a film structure corresponding to the filmstructure of FIG. 2B. Alternatively, the first extrudate 113 may be fedthrough a second encapsulator thereby encapsulating the first extrudateby the PE copolymer such as, for example, EMA, thereby making a filmstructure corresponding to the film structure of FIG. 2A.

Preferably, the adhesive layers 114, 130 are EMA. To adequately adherethe EMA to the oriented polypropylene layer, as shown in Structure 1,the EMA should be extruded at a temperature of about 550° F. Moreover,the adhesive layers 114, 132 bonded to the outer layer 120 of PET shouldbe extruded at a temperature of about 610° F. to adequately adhere tothe PET. As previously noted, the adhesive layers 112 protect the EVOHbarrier layer from the high temperatures or long residence times of theencapsulation or coextrusion of the adhesive layers 114, 130 and/or 132.

STRUCTURE 2 Layer Components Melt Temperature Outer Layer 118 EVA NAOuter Layer 116 OPP or biaxially oriented nylon NA Adhesive 114, 130LDPE, EMA or other PE 550-610° F. copolymers (with or without maleicanhydride functionality) Adhesive 112 Nylon 440-470° F. Barrier 110 EVOHor EVOH blend 400-450° F. Adhesive 112 Nylon 440-470° F. Adhesive 114,132 LDPE, EMA or other PE ˜610° F. copolymers (with or without maleicanhydride functionality) Outer Layer 120 PET or other NA

As shown in Structure 2 and corresponding to the film structure shown inFIG. 2A or 2B, EVOH or an EVOH blend (>75% EVOH) may be used as thebarrier layer 110 with nylon as the adhesive layers 112 encapsulatingthe EVOH barrier layer 110. The EVOH barrier layer may be extrudedwithin a temperature range of 400° F. and 450° F., preferably 410° F.and may be encapsulated by nylon that may be extruded within thetemperature range of 440 F. and 470° F., preferably 450°F. Next, theadhesive layers 114, 130 and/or 132 comprising a layer of LDPE or EMAmay encapsulate or otherwise be coextruded with the first extrudate 113of EVOH and nylon to make a film structure corresponding to the filmstructure of FIG. 2A or 2B. To adequately adhere the LDPE or EMA to theoriented polypropylene layer, as shown in Structure 2, the LDPE or EMAshould be extruded at a temperature of about 550° F. Moreover, theadhesive layers 114, 132 comprising LDPE or EMA bonded to the outerlayer 120 of PET should be extruded at a temperature of about 610° F. toadequately adhere to the PET. As previously noted, the adhesive layers112 protect the EVOH barrier layer from the high temperatures or longresidence times of the encapsulation or coextrusion of the adhesivelayers 114, 130 and/or 132.

STRUCTURE 3 Layer Components Melt Temperature Outer Layer 118 EVA orother NA Adhesive 114, 130 LDPE 580-620° F. Adhesive 112 Acid Terpolymer400-450° F. Barrier 110 EVOH 400-450° F. Adhesive 112 Acid Terpolymer400-500° F. Adhesive 114, 132 LDPE ˜610° F. Outer Layer 120 PET or otherNA

Structure 3 may correspond to the film structure of FIG. 2B, exceptwithout the outer layer 116. In other words, Structure 3 may have abarrier layer 110 of EVOH encapsulated by the adhesive layers 112comprising, preferably, acid terpolymer. Again, the EVOH and the acidterpolymer may be extruded between 400° F. and 450° F. Adhesive layers114, 130 and/or 132 may encapsulate or otherwise be coextruded with thefirst extrudate 113 comprising EVOH and acid terpolymer. The adhesivelayers 114, 130 bonding to outer layer 118 comprising EVA may beextruded at a temperature between 580° F. and 620° F. The adhesivelayers 114, 132 that bond to the outer layer 120 comprising PET may beextruded at a temperature of about 610° F. The elimination of the OPPlayers allows for the use of LDPE as the adhesive layer 114 or 130.

STRUCTURE 4 Layer Components Melt Temperature Outer Layer 118 EVA orother NA Outer Layer 116 OPP or biaxially oriented nylon NA Adhesive114, 130 PE with grafted maleic 580-620° F. anhydride Adhesive 112 Nylon440-470° F. Barrier 110 EVOH or EVOH/nylon blend 400-450° F. Adhesive112 Nylon 440-470° F. Adhesive 114, 132 PE with grafted maleic ˜610° F.anhydride Outer Layer 120 PET or biaxially oriented nylon NA

Structure 4 illustrates another preferred embodiment of the presentinvention. In this embodiment, the barrier layer 110 may be EVOH or EVOHblended with nylon having adhesive 112 comprising nylon encapsulatingthe barrier layer 110. Again, the barrier layer 110 and the firstadhesive layers 112 may be extruded and encapsulated at roughly the sametemperature to protect the barrier layer from degradation caused by heator long residence times. Further, the adhesive layers 114, 130 and/or132 may comprise polyethylene blended with polyethylene having maleicanhydride functional groups grafted thereto and may encapsulate thebarrier layer and the first adhesive layers or may otherwise becoextruded therewith. The adhesive layers 114, 130 and/or 132 may beextruded at a relatively high temperature compared to the barrier layerand the adhesive layers 112: about 580° F. to about 620° F. The outerlayer 116 may comprise an oriented polypropylene layer or a layer ofnylon disposed between the adhesive layer 114 or 130 and the outer layer118 may comprise a sealant layer of EVA or other material. Further, theouter layer 120 may be PET or biaxially oriented nylon. Anotherembodiment may have no outer layer 116 disposed between the adhesive 114or 130 and the outer layer 118.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications may be madewithout departing from the spirit and scope of the present invention andwithout diminishing its attendant advantages. It is, therefore, intendedthat such changes and modifications be covered by the appended claims.

We claim:
 1. A film structure comprising: a barrier layer comprisingethylene vinyl alcohol copolymer; first adhesive material encapsulatingsaid barrier layer and forming first and second adhesive layers disposedon opposite surfaces of said barrier layer wherein said first adhesivematerial is selected from the group consisting of acid terpolymer,polyolefin having maleic anhydride grafted thereto, and polyamide; athird adhesive layer disposed adjacent to said first adhesive layerwherein said third adhesive layer comprises a polyethylene orpolyethylene copolymer; a fourth adhesive layer disposed adjacent tosaid second adhesive layer wherein said fourth adhesive layer comprisesa polyethylene or polyethylene copolymer; a heat sealant layercomprising ethylene vinyl acetate copolymer disposed adjacent to saidthird adhesive layer; and an outer layer comprising polyester whereinsaid barrier layer and first, second, third and fourth adhesive layersare extrusion laminated to said outer layer.
 2. The film structure ofclaim 1 wherein said third and fourth adhesive layers are coextrudedfrom the same melt stream and encapsulate the barrier layer and firstadhesive material.
 3. The film structure of claim 1 further comprising:an oriented polypropylene layer disposed between the third adhesivelayer and the heat sealant layer.
 4. The film structure of claim 1wherein said third and fourth adhesive layers comprise low densitypolyethylene.
 5. The film structure of claim 1 wherein said third andfourth adhesive layers comprise polyolefin having maleic anhydridegrated thereto.
 6. A method of manufacturing a film structure, themethod comprising the steps of: providing a first extruder for extrudinga thermally sensitive barrier material; providing a second extruder forextruding a first adhesive material; encapsulating the barrier materialby the first adhesive material in a first encapsulator to form a firstextrudate at a temperature between about 400° F. and 450° F.; providinga second adhesive material; extruding the second adhesive material via athird extruder; adhering the first extrudate to the second adhesive at atemperature between about 550° F. and about 620° F. to form a combinedmeltstream wherein the second temperature is higher than the firsttemperature; feeding the combined meltstream through a die to form aflat sheet wherein the flat sheet includes a barrier layer encapsulatedby first adhesive layers on opposite sides of the barrier layer andfurther wherein at least one of the first adhesive layers are bonded toa second adhesive layer on an outside surface of the first adhesivelayers; and laminating said sheet to a substrate at a temperature higherthan the first temperature.